COLD weather alerts were in force across more than half of the US yesterday as the “polar vortex” of freezing Arctic air charged towards the east coast.

Forecasters warned of “dangerous temperatures” in the country’s worst cold snap for two decades.

In Comertown, Montana, the mercury plunged to -53C with the wind chill.

Residents of many states were warned they risk frostbite within minutes if they ventured outside. In Chicago, as temperatures fell to -27C, Lincoln Park Zoo’s lone polar bear, Anana, was moved indoors as she did not have enough body fat to withstand the cold.

A pedestrian crosses a snow-covered street in Chicago [REUTERS]

Al Fanslau works to clear the driveway of his home at the corner of in Michigan [AP]

The polar vortex, which has also gripped Canada, is expected to reach as far south as central Florida.

Across the US, public parks were shut and emergency shelters for the homeless were operating at maximum capacity. In Kentucky, an on-the-run convict gave himself in to police saying he could no longer endure the cold.

Thousands of flights have been grounded and in New York Governor Andrew Cuomo announced that major highways would be closed as temperatures were set to plunge to -26C.

The extreme weather has been blamed for 16 deaths, including four men shovelling snow in Illinois and a one-year-old boy in Missouri killed when a car hit a snowplough.

Icicles hang from the eaves of a houseas temperatures hover near 0 degrees [EPA]